1. Field of the Invention
The present invention relates to monoclonal antibodies to MUC1* and uses of thereof.
2. General Background and State of the Art
The MUC1 receptor is a Type I transmembrane glycoprotein from the mucin family that has been implicated in many human cancers. It is estimated that approximately 75% of all solid tumors aberrantly express the MUC1 receptor. The group of MUC1+ cancers includes more than 90% of breast carcinomas, 47% of prostate tumors and a high percentage of ovarian, colorectal, lung, and pancreatic cancers. There is some evidence that among the normal functions of the MUC1 receptor are roles in cell adhesion, fertility and immune response. The role of the MUC1 receptor in cancers has not yet been established in the literature. However, major differences in cell surface expression and receptor patterning in cancers have been well documented. The most striking difference between MUC1 expression on a healthy cell and expression in a cancer cell is that on a healthy cell, the receptor is clustered at the apical border, while on cancer cells the receptor is uniformly distributed over the entire surface of the cell. Additionally, there is some evidence that the receptor is overexpressed on tumor cells in addition to the aberrant patterning.
The normal function of MUC1 as well as its link to cancer has not yet been definitively determined. What is known is that a portion of the extracellular domain of MUC1 is shed or cleaved and can be detected in the serum of breast cancer patients. In breast cancer patients, levels of shed MUC1 in the serum are sometimes measured to monitor the patient's response to treatment. The cytoplasmic tail of MUC1 is rich in motifs for a variety of signal transduction proteins. It has been reported in the literature that Grb2 and SOS, which are common signaling proteins, associate with MUC1's cytoplasmic tail. It is noted in the scientific literature that in cancer cells, the extracellular domain is underglycosylated.
A membrane-bound MUC1 cleavage product, MUC1*, is the predominant form of the protein on cultured cancer cells and on cancerous tissues. MUC1* consists of the cytoplasmic tail, transmembrane domain, and about 45 amino acids of the extracellular domain (ECD). Although the exact site(s) of cleavage remain somewhat uncertain.
MUC1* stimulates cell growth when it is activated by ligand-induced dimerization. There are several instances when it is desirable to enhance the growth of certain cells and to this end, a convenient method for doing so is via the addition of a bivalent anti-MUC1* antibody, which simulates a dimeric ligand. In other cases, it is desirable to inhibit the growth of MUC1*-positive cells. For example, many cancer cells express MUC1*. The growth of MUC1-positive cancer cells is inhibited when a monovalent agent binds to MUC1* and prevents dimerization. A convenient monovalent agent for blocking MUC1*-mediated cell growth is a monovalent antibody. Monovalent antibodies can be antibody fragments that are enzymatic digestion products, or they can be engineered to have only one antigen binding site. Antibodies that bind MUC1* monovalently also include bispecific antibodies since they, too, inhibit dimerization of the extracellular domain of MUC1*. The stimulation (bivalent) and inhibition (monvalent) of MUC1*-mediated cell growth using polyclonal antibodies that recognize the primary sequence of MUC1 growth factor receptor (PSMGFR) sequence (SEQ ID NO:1) and variants thereof. Here, we disclose the generation of monoclonal antibodies that recognize the PSMGFR sequence and variants.
There are many reasons for identifying monoclonal antibodies. For example, a hybridoma that produces a single antibody species provides a reproducible supply of a single antibody, the monoclonal, rather than a collection of antibodies which have a variety of affinities, specificities and the generation of which is not totally reproducible. Each batch of antibodies comes from a different animal and a different immunization. By contrast, once a hybridoma is identified that produces an antibody with the desired characteristics, then by maintaining the hybridoma, one has an unlimited supply of a reproducible, single species antibody. Additionally, once a monoclonal or single species of antibody has been identified, one can determine the sequence of the antibody or its variable regions. This enables many forms of protein engineering and recombinant DNA technology which can be used for example to make antibody derivatives, including but not limited to single chain, bispecific, diabodies, and antibody-chemical fusions or antibody-protein fusions. For example, knowing the sequence of an antibody enables generating a monovalent, single chain antibody consisting of variable light and heavy chain regions connected by a linker sequence. Depending upon the target, it may also be desirable to generate a bispecific antibody wherein each variable region (heavy and light chain) recognizes a different target.